1 files changed, 51 insertions, 7 deletions

diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index a33e608713e9..8526008eba72 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -1437,13 +1437,50 @@ out_security_failure:
 }
 
 /*
+ * Match the requested auth flavors with the list returned by
+ * the server.  Returns zero and sets the mount's authentication
+ * flavor on success; returns -EACCES if server does not support
+ * the requested flavor.
+ */
+static int nfs_walk_authlist(struct nfs_parsed_mount_data *args,
+			     struct nfs_mount_request *request)
+{
+	unsigned int i, j, server_authlist_len = *(request->auth_flav_len);
+
+	/*
+	 * We avoid sophisticated negotiating here, as there are
+	 * plenty of cases where we can get it wrong, providing
+	 * either too little or too much security.
+	 *
+	 * RFC 2623, section 2.7 suggests we SHOULD prefer the
+	 * flavor listed first.  However, some servers list
+	 * AUTH_NULL first.  Our caller plants AUTH_SYS, the
+	 * preferred default, in args->auth_flavors[0] if user
+	 * didn't specify sec= mount option.
+	 */
+	for (i = 0; i < args->auth_flavor_len; i++)
+		for (j = 0; j < server_authlist_len; j++)
+			if (args->auth_flavors[i] == request->auth_flavs[j]) {
+				dfprintk(MOUNT, "NFS: using auth flavor %d\n",
+					request->auth_flavs[j]);
+				args->auth_flavors[0] = request->auth_flavs[j];
+				return 0;
+			}
+
+	dfprintk(MOUNT, "NFS: server does not support requested auth flavor\n");
+	nfs_umount(request);
+	return -EACCES;
+}
+
+/*
  * Use the remote server's MOUNT service to request the NFS file handle
  * corresponding to the provided path.
  */
 static int nfs_try_mount(struct nfs_parsed_mount_data *args,
 			 struct nfs_fh *root_fh)
 {
-	unsigned int auth_flavor_len = 0;
+	rpc_authflavor_t server_authlist[NFS_MAX_SECFLAVORS];
+	unsigned int server_authlist_len = ARRAY_SIZE(server_authlist);
 	struct nfs_mount_request request = {
 		.sap		= (struct sockaddr *)
 						&args->mount_server.address,
@@ -1451,7 +1488,8 @@ static int nfs_try_mount(struct nfs_parsed_mount_data *args,
 		.protocol	= args->mount_server.protocol,
 		.fh		= root_fh,
 		.noresvport	= args->flags & NFS_MOUNT_NORESVPORT,
-		.auth_flav_len	= &auth_flavor_len,
+		.auth_flav_len	= &server_authlist_len,
+		.auth_flavs	= server_authlist,
 	};
 	int status;
 
@@ -1488,12 +1526,18 @@ static int nfs_try_mount(struct nfs_parsed_mount_data *args,
 	 * to a file handle.
 	 */
 	status = nfs_mount(&request);
-	if (status == 0)
-		return 0;
+	if (status != 0) {
+		dfprintk(MOUNT, "NFS: unable to mount server %s, error %d\n",
+				request.hostname, status);
+		return status;
+	}
 
-	dfprintk(MOUNT, "NFS: unable to mount server %s, error %d\n",
-			request.hostname, status);
-	return status;
+	/*
+	 * MNTv1 (NFSv2) does not support auth flavor negotiation.
+	 */
+	if (args->mount_server.version != NFS_MNT3_VERSION)
+		return 0;
+	return nfs_walk_authlist(args, &request);
 }
 
 static int nfs_parse_simple_hostname(const char *dev_name,